Corner cutting method and NC controller

ABSTRACT

An NC controller determines a subsequent point sequence position in each sampling by interpolation calculation with a section between a corner cutting starting point and a corner cutting end point as a machined section. The NC controller then internally calculates a spindle rotating angle in a coordinate position where an outer end of a cutting edge is positioned at the subsequent point sequence position. Based on the spindle rotating angle and the substantial diameter of the rotary tool, the NC controller internally calculates coordinate values of the spindle at the subsequent point sequence position. Based on the coordinate values of the spindle, the rotary tool and a workpiece are relatively shifted on a plane parallel to the bottom surface of the tool while the spindle rotation is controlled in synchronization with the shifting, thereby cutting the corner.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to a method of cutting a corner as arecess or angle, and an NC (numerically controlling) controllertherefor.

[0003] 2. Description of the Related Art

[0004] For processing corners of a pocket such as a die cavity,conventionally employed is a cutting process by a rotary tool such as acylindrical end mill, or an electrical discharge process by a barelectrode or wire electrode.

[0005] Now focused is a cutting process by an end mill that isinapplicable to a corner R processing of a pocket having a cornerrecessed with a smaller radius of curvature than the tool radius. Givena minimum radius of curvature of a recessed corner, the end mill to beemployed for processing the corner needs a tool radius smaller than, andhence not exceeding at maximum, the given minimum radius. Still less, ifthe pocket is deep, the tool needs to have a long stem small indiameter, with an insufficient rigidity for the cutting to be proper.Yet, the end mill is inapplicable to processing an angled corner with asharp angle, such as 90°, called “pin angle”.

[0006] Accordingly, for such a processing as to a pin angle or a pocketwith deep recessed corners small of radius of curvature, the electricaldischarge process is typically employed, which however is less efficientand dearer in cost than the cutting process, thus leading to adesideratum for a process to be complete with a single machine tool,without needing the electrical discharge as a different process, for asuccessful reduction of process lead time.

SUMMARY OF THE INVENTION

[0007] This invention was made as a solution to such problems. Ittherefore is an object of the invention to provide a corner cuttingmethod and an NC controller therefor, allowing for the cutting to beefficient in application to a corner processing such as of a pocket withdeep recessed corners small of radius of curvature (minute R), or of anangled corner with a sharp angle, such as 90°, called “pin angle”.

[0008] According to an aspect of this invention, there is provided acorner cutting method in which a rotary tool having a cutting edge atleast on a bottom surface thereof and on an outer periphery thereof isused, the rotary tool and a workpiece are relatively shifted on a planeparallel to the bottom surface of the tool so that an outer end of thecutting edge of the rotary tool rotated by a spindle creates a shiftingpath meeting a desirable shape of a corner to be machined, and therotary tool is shifted while cutting in an axis direction of the rotarytool, the method comprising the steps of: inputting information oncoordinate values and a direction and an angle of a corner to bemachined and information on the rotary tool, to an NC controller;internally calculating coordinate values at a corner cutting startingpoint where the outer end of the cutting edge is positioned, and aspindle rotating angle in this position, and coordinate values of acorner cutting end point, based on the input information; internallycalculating a spindle rotating angle at a coordinate position where theouter end of the cutting edge is positioned at a subsequent pointsequence position in each sampling, the subsequent point sequenceposition being obtained by an interpolation calculation, letting asection between the corner cutting starting point and the corner cuttingend point be a section to be machined; internally calculating coordinatevalues of the spindle at the subsequent point sequence position based onthe spindle rotating angle and a substantial diameter of the rotarytool; and relatively shifting the rotary tool and the workpiece based onthe coordinate values of the spindle on a plane parallel to the bottomsurface of the tool while controlling the spindle rotation insynchronization with the shifting.

[0009] The above method thus allows effective machining of a deep pocketwith corners of a small radius of curvature or a corner of 90 degrees orless while maintaining sufficient rigidity of the tool.

[0010] According to another aspect of this invention, the interpolationcomprises one of a linear interpolation, a circular interpolation, afree-form curve interpolation, and an arbitrary combination thereof.

[0011] Thus the interpolation may be any existing interpolation.

[0012] According to yet another aspect of this invention, there isprovided an NC controller for implementing a corner cutting methodaccording to either of the above aspects, comprising: an analyzer foranalyzing a machining program comprising commands for implementing thecorner cutting method, the commands being set as one code of G function.

[0013] Thus the method does not depend on a macro program with a dividedpoint-shifting block sequence made as another program, allowingefficient machining in a smooth cutting-edge path at a high cuttingspeed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The above and further objects and novel features of thisinvention will more fully appear from the following detailed descriptionwhen the same is read in conjunction with the accompanying drawings, inwhich:

[0015]FIG. 1 is a perspective illustration of a machine tool forimplementing a corner cutting method embodying this invention;

[0016]FIG. 2 is a perspective view of a rotary tool to be used in theembodying method, as it is in an inverted position with a bottomoriented upward,

[0017]FIG. 3 is a bottom view of the rotary tool;

[0018]FIG. 4 is a plan as an illustration of a corner cutting in theembodying method;

[0019]FIGS. 5A to 5C are plans illustrating a process of cutting a90-degree corner in the embodying method;

[0020]FIG. 6 is a graph plotting a tool moving path in the cutting of90-degree corner;

[0021]FIG. 7 is an illustration showing a direction and an angle of acorner;

[0022]FIGS. 8A to 8C illustrate various rotary tools applicable to theembodying method;

[0023]FIG. 9 is an illustration of a corner cutting method according tocorner cutting code G180 (G181);

[0024]FIG. 10 is a functional block diagram of an NC controlleraccording to an embodiment of this invention;

[0025]FIG. 11 is a flow chart of a corner cutting process by the NCcontroller;

[0026]FIG. 12 is an illustration of a corner cutting method according toanother embodiment of this invention;

[0027]FIG. 13 illustrates another rotary tool applicable to thisinvention; and

[0028]FIG. 14 illustrates another rotary tool applicable this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] There will be detailed below the preferred embodiments of thisinvention with reference to the accompanying drawings. Like members aredesignated by like reference characters.

[0030]FIG. 1 shows a machine tool for use in a corner cutting methodaccording to this invention. The machine tool has an X-axis table 1movable in the X-axis direction, a Y-axis table 2 movable in the Y-axisdirection mounted on the X-axis table, a headstock 3 movable in theZ-axis direction and a spindle 4 attached to the headstock 3. Aworkpiece W is set on the Y-axis table.

[0031] The X-axis table 1 is shifted in the X-axis direction by anX-axis feed mechanism 6 driven by an X-axis servomotor 5. The Y-axistable 2 is shifted in the Y-axis direction by a Y-axis feed mechanism 8driven by a Y-axis servomotor 7. The headstock 3 is shifted in theZ-axis direction by a Z-axis feed mechanism 10 driven by a Z-axisservomotor 9. Rotary encoders 11, 12 and 13 for position detection aremounted to the X-, Y- and Z-axis servomotors 5, 7 and 9, respectively.

[0032] The spindle 4 is driven by a spindle motor 14. A rotary encoder15 mounted to the spindle motor 14 detects an angle of rotation (C-axisangle) of the spindle 4. A rotary tool 50 is attached to the spindle 4.

[0033] The machine tool may be of a numerical control type. An NCcontroller 20 is input position information and C-axis angle informationfrom the rotary encoders 11, 12, 13 and 15 of the respective axes, andcontrols the rotational driving of the spindle 4 by the spindle motor 14and the driving of the servomotors 5, 7 and 9 of the respective axes.

[0034]FIGS. 2 and 3 show a rotary tool to be used in the embodimentaccording to the this invention. In FIG. 2, the rotary tool is seen inan inverted position with a bottom oriented upward, and FIG. 3 is abottom view of the rotary tool.

[0035] The rotary tool used in the embodying method has a polygonalbottom surface such as a triangular, quadrangular or pentagonal surface,having at least one cutting edge at the bottom and one on the outerperiphery. A rotary tool 50 as shown in FIGS. 2 and 3 has a regulartriangular bottom surface 51. Each side of the triangular bottom 51 hasa cutting edge 52, 53 or 54 extending half the length of the side to thevertex “a”, “b” or “c” (outer ends of the cutting edge) of the triangle.Clearance angles (flanks 55, 56 and 57) are provided rearward of thecutting edges. The cutting edges 52, 53 and 54 also extend the length ofthe peripheral ridges extending from the vertices “a”, “b” and “c” inthe axis direction.

[0036] The rotary tool 50 also has a trunk 58 in a cylindrical shapeextending along the axis line passing the internal center of the regulartriangular bottom surface 51. The trunk 58 is held by a chuck (notshown) of the spindle 4 and is driven to rotate in the counterclockwisedirection around the axis line in FIGS. 2 and 3.

[0037]FIG. 4 shows the rotary tool 50 used for cutting off remainingparts (hatched) of corners (internal angles) of a workpiece W whilebeing shifted along the corner sides. The rotary tool 50 is also rotatedby the spindle 4 in correspondence with the shifting.

[0038] In this corner cutting method, the NC controller 20 is givenvertex coordinate values (Xo, Yo) as shown in FIGS. 5A to 5C andinformation on a direction and an angle of a corner to be machined, andinformation on the rotary tool 50. Based on the information, the NCcontroller 20 internally calculates coordinate values of corner cuttingstarting points S1, S2, i.e., (Xs1, Ys1), (Xs2, Ys2), at which any ofthe vertices (outer ends) “a”, “b” and “c” of the cutting edges 52, 53and 54 is positioned at Pc, spindle rotating angles in the coordinates,and coordinate values of corner cutting end points E1, E2, i.e., (Xe1,Ye1), (Xe2, Ye2). Then, a subsequent point sequence position in eachsampling is determined by linear interpolation calculation with each ofthe interval between the starting point S1 and the end point E1 and theinterval between the starting point S2 and the end point E2 as amachined section. The NC controller 20 internally calculates a spindlerotating angle at a coordinate position where any of the vertices (outerends) of the cutting edges 52, 53 and 54 is positioned at the determinedsubsequent position Ps. From this spindle rotating angle and thesubstantial diameter of the rotary tool 50, the NC controller 20internally calculates coordinate values of the spindle 4 at thedetermined subsequent position. Based on the coordinate values of thespindle 4, the X-axis table 1 and the Y-axis table 2 are shifted in therespective axis directions so as to relatively shift the rotary tool 50and the workpiece W on a plane parallel to the bottom surface of thetool. In synchronization with the shifting, the rotation of the spindle4 is controlled to machine the corner.

[0039] The interpolation is not limited to the linear interpolation, andmay be circular interpolation, free-form curve interpolation, or anycombination thereof. Circular interpolation is used to machine roundcorners.

[0040] The above-described corner cutting method allows cutting a roundcorner of a small radius of curvature with a tool of a radius greaterthan that of the round corner. Further the method enables cutting of aright angle, which is larger than the internal angle of the polygonalbottom surface 51. The rotary tool 50 with the regular triangle bottomsurface has an internal angle of 60 degrees, so that the tool can cut aright angle as shown in FIG. 6. FIG. 6 shows a moving path of the toolwhen machining a right angle. In the figure, reference sign Cc denotesthe shape of the corner before machining. The area surrounded by theimaginary line Cc, the X-coordinate axis line and the Y-coordinate axisline is to be removed by the machining. Designated by referencecharacter Dr is the direction of tool rotation.

[0041] In this example, the rotary tool 50 rotates 120 degrees is acycle. Upon one cycle, the subsequent edge is positioned at a startingpoint S1. Thus repetition of the above machining cycle enablescontinuous corner cutting. Shifting the rotary tool 50 cutting in thedepth direction in a cycle or upon completion of cycles allows themachining of a deep corner.

[0042] The NC controller 20 analyzes a machining program consisting ofcommands for implementing the corner cutting method, set as a code of Gfunction, G180 (CW direction), G181 (CCW direction), for example,thereby implementing the method. An exemplary format of G180 (G181) isas follows:

G180 (G181) Xo_Yo_A_B_Zo_Z_Q_P_K_(:r)F_, in which:

[0043] Xo, Yo are corner vertex coordinate values (ABS/INS);

[0044] A is a corner direction (+an angle between an X-axis directionand a corner position) (See FIG. 7);

[0045] B is a corner angle (See FIG. 7);

[0046] Zo is a clearance point in a Z-axis direction (ABS/INS);

[0047] Z is a depth end point in the Z-axis direction (ABS/INS);

[0048] Q is a cutting amount in a depth direction;

[0049] P is a shape of a cutting tool (2: two-vertices tool; 3: triangletool; 4: quadrangle tool) (See FIGS. 8A to 8C);

[0050] K is the length of one side of the cutting tool (See FIGS. 8A to8C);

[0051] :r is a round of a corner (no round when not specified); and

[0052] F is an edge cutting speed (when specified, subsequent F is thespecified one).

[0053] Now, with reference to FIG. 9, the corner cutting based on thecorner cutting code G180 (G181) will be described.

[0054] The substantial radius R of the cutting tool 50 is expressed asR=K/(2 cos γ) derived from K=2R cos γ. γ depends on P specified, and is0 degree in a two-vertices tool, 30 degrees in a triangular tool, and 45degrees in a quadrangular tool.

[0055] Here, corner angle B is not less than 90 degrees, and the cuttingedge is shifted from S1 through (Xo, Yo) to E2.

α=(180−B)/2

C=A+180−(B/2)

L1 cos α=K/2

Hence, L1=K/(2 cos α)

L2 cos α=K/2

Hence, L2=K/(2 cos α)

[0056] The starting point is indicated as (Xs1, Ys1), the corner vertexcoordinates (Xo, Yo), and the end point (Xe2, Ye2).

Xs1=Xo+L1 cos C

=Xo+K cos C/2(cos α)

Ys1=Yo+L1 sin C

=Yo+K sin C/(2 cos α)

Xe2=Xo+L2 cos(B+C)

=Xo+K cos(B+C)/2(cos α)

Ys1=Yo+L2 sin(B+C)

=Yo+K sin(B+C)/(2 cos α)

[0057] The spindle angle at (Xo, Yo) is expressed as θo. The spindleangle at the starting point (Xs1, Ys1) is expressed by θo+θe. θe is(90−γ), and is 90 degrees in the two-vertices tool, 60 degrees in thetriangular tool, and 45 degrees in the quadrangular tool.

[0058] The spindle angle θ new when the cutting edge is shifted by Lleadon a path from the starting point is expressed with the remainingshifting amount Ldist to the end point.

Ldist=L1(or L2)−Llead

θnew=A+(Ldist/L1(or L2))G

[0059] Initially, Ldist=L1(or L2). G is the spindle rotating angle fromthe starting point to the corner vertex.

[0060] The spindle rotating angle Δθ in each sampling is expressed as:

Δθ=θnew−θold

[0061] θ old is a spindle rotating angle one sampling before.

[0062] Coordinates (Xt, Yt) of a tool edge shifting on the path isexpressed as follows:

[0063] I. From the starting point S1 to the corner vertex position (Xo,Yo)

Xt=Xo+Ldist·cos C

Yt=Yo+Ldist·sin C

[0064] II. From (Xo, Yo) to the end point E2

Xt=Xo+Ldist·cos(B+C)

Yt=Yo+Ldist·sin(B+C)

[0065] The spindle center coordinates (Xsp, Ysp) is expressed asfollows:

Xsp=Xt+R cos θnew

Ysp=Yt+R sin θnew

[0066] Spindle position distributing amounts ΔXsp, ΔYsp during onesampling are expressed as follows:

ΔXsp=R cos θnew−R cos θold

ΔYsp=R sin θnew−R sin θold

[0067] The spindle rotating angle Δθ and the spindle positiondistributing amounts ΔXsp, ΔYsp are specified every sampling to theservomotors 5, 7 and the spindle motor 14 for corner cutting.

[0068] The machining may be implemented by a macro program with adivided point-shifting block sequence made as another program. However,the machining based on the corner cutting code G180 (G181) does notdepend on the number of blocks divided, allowing more effective cuttingin a smoother cutting edge path at a higher speed as compared with themachining by such a macro program.

[0069]FIG. 10 shows the architecture of the NC controller 20. The NCcontroller 20 is input a machining program by a machining programspecifying section 31 of an input device 30, and stores the machiningprogram in a machining program memory 21. The NC controller 20 includesa machining program executing section 22, XYZ position calculatingsection 23, and spindle position calculating section 24 implemented by acomputer.

[0070] The executing section 22 reads the machining program from thememory 21, and analyzes the program to execute. The XYZ positioncalculating section 23 calculates control target values of the X, Y andZ axes based on the data from the executing section 22. The spindleposition calculating section 24 calculates a control target value of thespindle position (spindle rotating angle) based on data from theexecuting section 22 and data from the XYZ position calculating section23. These control target values are outputted to an output controller25. The output controller 25 controls the driving of the servomotors 5,7 and 9 and the spindle motor 14 based on the control target values.

[0071] Now, the process of corner cutting with the NC controller 20 willbe described with reference to a flow chart shown in FIGS. 11.

[0072] The first step is to read the machining program from themachining program specifying section 31 to store it in the machiningprogram memory 21 (step S11). Then in the machining program executingsection 22, the program is analyzed and executed, and control commandsrequired for desired machining are outputted to the XYZ positioncalculating section 23 (step S12).

[0073] Next, based on the control commands from the executing section22, the spindle 4 is rotated to a machining starting angle (initialangle) (step S13), and the rotary tool 50 is positioned at the startingposition (initial position) (step S14). Then, based on the controlcommands from the executing section 22, the rotary tool 50 is positionedat Zo point (clearance point in the Z-axis direction) (step S15).

[0074] Next, based on the control commands from the executing section22, machining is performed, synchronizing the shifting of the workpieceW in the X-, Y-axis directions and the rotation of the spindle 4 (stepS16). It is determined whether the Z-axis direction reaches the finalcutting position (hole bottom position) (step S17). When the decision isNO, the cutting in the Z-axis direction is carried out (step S18). WhenYES, the rotary tool 50 is returned to the initial position (step S19).

[0075] Instead of shifting the workpiece W in the X- and Y-axisdirections, the rotary tool 50, that is, the headstock 3 may be shiftedin the X- and Y-axis directions.

[0076] The above-described machining with the triangular tool is limitedto the corner from the starting point S1 to the end point E2. In somecases, however, a wider area extending before the starting point S1 andafter the end point E2 is to be machined as shown in FIG. 12. In thesecases, the rotary tool 50 is shifted while cutting without rotation ofthe spindle 4 in a section from P1 to P2. In a section from P2 to P3,the above-described corner cutting is performed with the shifting of therotary tool 50 and the rotation of the spindle 4, synchronized to oneanother. In a section from P3 to P4, the rotary tool 50 is shifted whilecutting without rotation of the spindle 4. Thus the wider area extendingbefore the starting point S1 and after the end point E2 can becontinuously machined.

[0077] Cutting edge angles with respect to the workpiece in the sectionsfrom P1 to P2 and from P3 to P4 may be arbitrarily set in accordancewith the shape of the tool cutting edge, the material of the workpiece,and the like. The sections from P1 to P2 and from P3 to P4 are notlimited to linear ones. Any path may be specified as desired.

[0078] When the front shape of the rotary tool 50 is tapered as shown inFIG. 13, an inclined corner surface can be machined. When the front endof the rotary tool 50 is shaped as desired as shown in FIG. 14, variousshapes of machined surfaces are obtained.

[0079] While preferred embodiments of the present invention have beendescribed using specific terms, such description is for illustrativepurposes, and it is to be understood that changes and variations may bemade without departing from the spirit or scope of the following claims.

What is claimed is:
 1. A corner cutting method in which a rotary toolhaving a cutting edge at least on a bottom surface thereof and on anouter periphery thereof is used, the rotary tool and a workpiece arerelatively shifted on a plane parallel to the bottom surface of the toolso that an outer end of the cutting edge of the rotary tool rotated by aspindle creates a shifting path meeting a desirable shape of a corner tobe machined, and the rotary tool is shifted while cutting in an axisdirection of the rotary tool, the method comprising the steps of:inputting information on coordinate values and a direction and an angleof a corner to be machined and information on the rotary tool, to an NCcontroller; internally calculating coordinate values at a corner cuttingstarting point where the outer end of the cutting edge is positioned,and a spindle rotating angle in this position, and coordinate values ofa corner cutting end point, based on the input information; internallycalculating a spindle rotating angle at a coordinate position where theouter end of the cutting edge is positioned at a subsequent pointsequence position in each sampling, the subsequent point sequenceposition being obtained by an interpolation calculation, letting asection between the corner cutting starting point and the corner cuttingend point be a section to be machined; internally calculating coordinatevalues of the spindle at the subsequent point sequence position based onthe spindle rotating angle and a substantial diameter of the rotarytool; and relatively shifting the rotary tool and the workpiece based onthe coordinate values of the spindle on a plane parallel to the bottomsurface of the tool while controlling the spindle rotation insynchronization with the shifting.
 2. A corner cutting method accordingto claim 1, wherein the interpolation comprises one of a linearinterpolation, a circular interpolation, a free-form curveinterpolation, and an arbitrary combination thereof.
 3. An NC controllerfor implementing the corner cutting method according to claim 1 or 2,comprising: an analyzer for analyzing a machining program comprisingcommands for implementing the corner cutting method, the commands beingset as one code of G function.